Project Summary Interleukin (IL)-4 plays a central role in the regulation of immune homeostasis and in various immune-mediated diseases including but not limited to asthma, allergies, tuberculosis, and autoimmunity-associated interstitial lung disease (scleroderma, rheumatoid arthritis, poly- and dermatomyositis). We recently described a splice variant of IL-4, so-called IL-442. The biology of IL-442 appears to be very different from that of IL-4, however the functions of this variant are still poorly understood. We found that the expression levels of IL-442 are dramatically increased in various diseases, including in asthma, to levels that are similar to or exceed those of IL-4. Furthermore, we recently found that IL-442 changes expression levels of numerous genes in human T cells, and that the IL-442-induced changes in the expression profile differ from those induced by IL-4. Unlike IL- 4, IL-442 does not stimulate phosphorylation of STAT6 in a broad range of tested concentrations. Similar to IL- 4, IL-442 stimulates phosphorylation of Jak1, Jak3, and Tyk2 in T cells in a time- and dose-dependent fashion. Gene delivery of IL-442 to mouse lungs causes proinflammatory changes in pulmonary milieu, with the induced levels of TNF-1, IL-11, IFN-3, IL-12p40, and MCP-1 significantly exceeding those induced by gene delivery of IL-4. In bronchoalveolar lavage and blood T cells of patients with asthma, relative expression levels of IL-442 were in many cases higher than those of IL-4. We also discovered that IL-442 potently stimulates production of MCP-1 in human T cells and even more potently (by several hundred fold) upregulates IL-442 production in autocrine fashion. Based on our preliminary data, the Specific Hypothesis of this study is that IL-442 binds to a specific cell surface receptor on T cells; activates characteristic intracellular signaling that is different from signaling induced by IL-4; changes gene expression in a fashion different from that induced by IL-4, particularly stimulating its own production in autocrine fashion; and ultimately stimulates production of numerous proinflammatory and Th1 molecules. Furthermore, the hypothesis is that IL-442 causes significant proinflammatory changes in the lungs in vivo, and is associated with more severe asthma in human patients. In Specific Aim 1, the effects of IL-442 on primary human lymphocytes, as well the regulation of its production at the molecular level, will be investigated in cell culture. In Specific Aim 2, effects of IL-442 gene delivery in vivo will be investigated in normal mice as well as in an ovalbumin-sensitized mouse model of asthma. In Specific Aim 3, the association of IL-442 with disease severity in asthma patients will be studied. This study is directly relevant to Veterans Healthcare. Many of the IL-4-mediated diseases have no known cures and are widely spread in the general population and particularly in veterans. These diseases are chronic, severe, debilitating, and even deadly. The strengths of this investigation are that it addresses a novel topic in a mechanistic way; that it combines mechanistic studies in cell culture, in experimental animals, and in human patients; and that it deals with a molecule that is involved in the mechanisms of numerous diseases that are prevalent in veterans. This study is expected to generate a wealth of novel information on IL-442 as a potential diagnostic marker as well as important target for future therapeutic modulation of numerous diseases in veterans.